Faster multiarch docker builds

* Use GOOS=$TARGETOS GOARCH=$TARGETARCH to cross compile
  instead of emulating the target architecture.

Author: nckturner

Dockerfile

@@ -13,10 +13,10 @@
 # limitations under the License.
 ARG image=public.ecr.aws/eks-distro-build-tooling/eks-distro-minimal-base-nonroot:2021-12-01-1638322424
 
-FROM golang:1.16 AS builder
+FROM --platform=$BUILDPLATFORM golang:1.16 AS builder
 WORKDIR /go/src/github.com/kubernetes-sigs/aws-iam-authenticator
 COPY . .
-RUN make bin
+RUN GOOS=$TARGETOS GOARCH=$TARGETARCH make bin
 RUN chown 65532 _output/bin/aws-iam-authenticator
 
 FROM public.ecr.aws/eks-distro/kubernetes/go-runner:v0.9.0-eks-1-21-4 as go-runner

cloudbuild.yaml

@@ -1,6 +1,3 @@
-images:
-  - 'gcr.io/$PROJECT_ID/aws-iam-authenticator:$_GIT_TAG'
-  - 'gcr.io/$PROJECT_ID/aws-iam-authenticator:latest'
 options:
   substitution_option: ALLOW_LOOSE
 steps: